Rock drills



Oct. 14, 1969 MAsAMlTsU'lsHH-ARA 3,472,128

nocx DRILLs Filed Jan. 12. 1968 7 j f 'a7 f l 1| 22 "l li' 2 r 5 l Il n:

E Y 44 3a l l f5r E l l; FIG. 24 ,'g l 5 y United States Patent O 3,472,128 ROCK DRILLS Masamitsu llshihara, Kannamimachi, Shizuoka-ken, Japan, assigner to Ishihara Kikai Kogyo Co., Ltd., Numazu, Japan, a corporation of Japan Filed Jan. 12, 1968, Ser. No. 697,347 Claims priority, application Japan, Aug. 12, 1967,

42/69,514 Int. Cl. Flj 1/10, 11/06 US. Cl. 92-172 2 Claims ABSTRACT F THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to a rock drill utilizing an internal combustion engine and more particularly to a percussion type rock drill wherein the drilling member is actuated by alternate application of the forces derived from engine explosion `and compressed air.

The engine cylinder of the prior art rock drill of the type referred to the above is generally made of castings such as those of cast steel commonly termed cylinder steel. However, where such a rock drill is used in the tropical or subtropical zone, there is the danger of the piston being seized due to overheating, because such castings have low radiating efficiency. Consequently required cooling causes the frequent interruption of operation of the rock drill, thus reducing its operating efficiency.

For improvement in the heat radiating efliciency, light metal alloys such as the known aluminum alloys developed in the automobile industry are deemed usable, and those aluminum alloys are indeed very effective for reduction of weight which is -most demanded of `a handworked rock drill.

However, though the engine cylinder may be made of an aluminum alloy, the hammer piston should be formed from steel material, because it is required to have suflcient strength and weight to impart percussion to the drilling member, for example, a chisel. However, the different thermal expansion coefficients of the engine cylinder and hammer piston will raise problems in this respect, More specifically, the problem lies in the fact that elevated temperatures will expand the space between the inner surface of the cylinder and the outer surface of the piston to reduce the engine efficiency.

To minimize decrease in the engine efciency, there is demanded rigid manufacturing tolerance for a cylinder and piston, particularly extremely high precision for their engagement, thus causing product yield to be lowered. Moreover, the piston ring engaged with the hammer pis- ICC ton is often destroyed by being llocally subjected to impact loads caused by the drilling of rocks.

SUMMARY OF THE INVENTION The present invention has been accomplished to eliminate the aforementioned drawbacks. Its object is to provide a novel rock drill which has improved durability against impact loads and is capable of maintaining the prescribed engine etliciency regardless of rises in the cylinder temperature through substantial elimination of difference in thermal expansion coefficient between the cylinder` and piston.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, in which:

FIG. l is a side elevation, partly in section, of a preferred embodiment of a rock drill constructed in accordance with this invention; and

FIG. 2 shows a longitudinal section of a modified hammer piston.

There will now be described the construction `and operational sequence of the rock drill by reference to FIG. 1. This rock drill is of the type driven by a two-cycle internal combustion engine. Namely, an engine cylinder 1 having a crank case connected to the upper part thereof comprises, as is known, an engine piston 2 and a hammer piston 3 slidably fitted into the upper and lower parts respectively.

The lower end of a connecting rod 4 is pivoted to the pin of the engine piston 2, and a crank shaft is horizontally journalled to the crank case. To the crank pin there is pivoted the upper end of the connecting rod 4. A blower cylinder 6 of an air compressor is contained in the upper portion of the crank case, said cylinder 6 slidably receive ing a piston 7 carrying a pin 7a which is pivotally connected to one end of a separate connecting rod 8. The other end of the connecting rod 8 is pivotally connected to the other crank pin 5a of the crank shaft 5. The space in the cylinder defined between the piston 2 and the hammer piston 3 when the former is in its upper dead center (in the position shown in the drawing) operates as a combustion chamber and an ignition plug (not shown) is provided on the portion of the inner wall of the cylinder involved in the combustion chamber. The hammer piston 3 is a so-called free piston and has a flange 9 and a hammer 10 integrally provided at its lower end. At the lower end of the engine cylinder 1 is integrally formed a coaxial cylinder 1a of larger diameter to form a pneu- `matic operating vchamber in conjunction with `a portion of the lower housing of the rock drill, said cylinder 1a being adapted to slidably receive said flange 9 of the hammer. The lower housing is provided with a cylinder 11 adapted to guide the hammer 10 and the head of a drilling member 12 is disposed at the lower end of the cylinder 11 to oppose the head of the hammer 10. A through opening 3a is drilled through the hammer piston 3 at right angles to its longitudinal axis and a through opening 13 is drilled along said axis to extend between the lower end of the hammer 10 and the transversal opening 3a. As shown in FIG. l, a main inlet port 14 and an auxiliary inlet port 14 are provided through the wall of the cylinder 1a on the left-hand side thereof, and an exhaust port 1S on the right-h-and side. The inlet ports 14 and 14 communicate with the outlet port of the compressor via a conduit 16 and the exhaust port 15 with an opening 18 at the lower end of the cylinder 11 via a passage 17 drilled through the middle housing.

The drilling member 12 is provided lwith an air opening 19 at its outer end to supply compressed air and is removably mounted on the boss of a gear 20 rotatably supported in the lower housing to mesh with a gear 21 vertically journalled to one side of the lower housing. A worm wheel 22 is secured to the upper end of a transmission shaft 21 of the gear 20 to be journalled to the upper housing. Said worm wheel 22 is meshed with a worm 23 secured to the crank shaft 5.

With the respective pistons positioned as illustrated, mixtures of compressed fuel and air are ignited to actuate the engine piston and hammer piston by the resulting explosion pressure. Thus the compressor compresses air by the action of its piston 7 and the hammer piston strikes the head of drilling member 12 with its hammer 10.

Thereafter, the engine piston continues retraction to open the exhaust and suction ports, thus performing scavenging and suction as is observed in the conventional two-cycle internal combustion engine. Then the piston operates inversely from the lower dead center to restart compression.

On the other hand, when the hammer piston completes striking, the periphery of the llange 9 is displaced from the inlet port 14 and exhaust port 15, so that the piston is now actuated in the opposite direction due to the compressed air from the compressor being introduced from an opening 18 into the cylinder 11 via the inlet port 14, space above the ange 9, export port and passage 17.

When the reverse motion proceeds the ilange, whose circumferential surface has plugged the port 14 is transferred upward to open the port 14. At this time compressed air is supplied directly to the underside through the port 14'. Since the pressure of the compressed air is applied over the entire underside of the ange, reverse motion will have a greater force.

Further, compressed air is supplied to the air opening 19 of the drilling member 12 via the transversal through opening 3a and the vertical through opening 13 at the time the hammer strikes the drilling member 12 and through the cylinder 11 when the hammer moves in the opposite direction. The volume of the space above the flange 9 is reduced without any resistance from the time when the inlet port 14 is closed by the periphery of the flange until the exhaust port 15 and the through opening 3a are closed with respect to said space. However, when the space above the ange 9 becomes completely sealed, in other words, when the flange 9 assumes the position shown in the drawing, the sealed space acts as an air cushion or damper. A similar air cushion is also formed at the lower end of the air operating chamber, such air cushion being formed when the space below the ange 9 is interrupted from the exhaust port 15 by the periphery of the flange 9, that is, when the hammer strikes the head of the drilling member. Further, the drilling member is rotated by the gear which is driven at a substantially reduced speed due to the rotation of the crank shaft 5.

There will now be described the particulars of the aforementioned rock drill which are involved in the present invention. The engine cylinder 1 is made of a light metal alloy of excellent heat radiation, such as aluminum alloy, and the inner wall of the engine cylinder 1 is plated with hard metal alloy, such as hard chromium. The hammer piston 3 is comprised of a pillar like member 24 serving as a core metal and a cylindrical member 2S shrinkage tted thereto. The piller like member 24, as well as the hammer 10, is made of steel, Whereas the cylindrical member 25 is made of the same alloy as the engine cylinder 1 or a similar alloy having substantially the same coefficient of thermal expansion. Preferably on the inside of the upper end of the cylindrical member 25 lthere is formed an annular groove with which is engaged a retaining ring 25 made of iron. The ring 26 itself is also provided with an annular groove into which brazing material consisting of stainless steel is cast to secure the pillar like member 24 and ring 26 to each other.

The diameter of a hammer piston in practical use is of the order of 60 mm. In the present invention, however, the diameter of a pillar like member and thc wall thickness of a cylindrical member have been experimentally determined which are required to have a thermal expansion coefficient substantinally the same as that of the engine cylinder and a sumcient strength to withstand the impact load applied by the hammer.

These experiments show that a pillar like member made of steel and having a diameter of 20 mm., and a cylindrical member made of the same material as the engine cylinder and having a wall thickness of 2() mm. are most suitable for use with an engine cylinder made of a light metal alloy and having a wall thickness of l0 mm., the practical range being from a minimum of 15 mm. to a maximum of 25 mm. for the diameter of the pillar like member and from a maximum of 22.5 mm. to Ia minimum of 17.5 mm. for the wall thickness of the cylindrical member.

Thus it may be generalized that it will be sutiicient to construct the hammer piston in such a manner that the diameter of the pillar like member and the wall thickness of the cylindrical member have substantially the same value.

Referring now to FIG. 2 showing another embodiment of the present invention, the outer diameter of the pillar like member 124 of the hammer piston 103 is 40 mm., and the diameter of the cylindrical member 25 thereof is 60 mm. The cylindrical member 125 is closed at the upper end and has a wall'thickness of 10 mm. The pillar like member 124 has -a tapered groove 130 provided inside which has an opening diameter of about 30 mm. and a bottom diameter of about 20 mm. The groove 130 constitutes an air chamber at a point where air passages 103a and 113 intersect each other. In this embodiment, the Wall thicknesses of the pillar like member and the cylindrical member are substantially equal. Further, the cylindrical member is firmly secured to the pillar like member by shrinkage fit alone.

Thus, use of an engine cylinder and hammer piston having the same thermal expansion coeflicient enables the space between the piston and cylinder to be always lixed independently of temperature rises in operation, thus preventing reduction in the engine efficiency.

High heat radiating efficiency resulting from use of light metal alloys permits long continuous use, and absence of a piston ring completely eliminates the danger of its damage which has always posed problems with the hammer piston subjected to impacts.

Furthermore, the fact that the engine cylinder and hammer piston according to the present invention have the same thermal expansion coeicient greatly relieve restrictions on the manufacturing tolerance relative to their diameters, thus serving to cut their manufacturing cost.

For improved wear resistance, the outer surface of the hammer piston may be plated with metal material such as hard chromium as is the inner surface of the engine cylinder.

It should be understood that the invention is not limited to the particular embodiments shown and described herein and that various modifications may be made with out departing from the true spirit of the invention.

What is claimed is:

1. A rock drill comprising an engine cylinder, and a hammer piston including a hammer made of steel, and adapted to strike a drilling member, said engine cylinder being made of a light metal alloy of high heat radiation, said hammer piston consisting of a pillar like member also made of steel and a cylindrical member made of the 5 same light metal alloy as the engine cylinder or a similar light metal alloy having substantially the same c0- eicient of thermal expansion, the cylindrical member being shrinkage tted to said pillar like member, and the Wall thickness of said cylindrical member being substan- 5 tially the same as the wall thickness or diameter of said pillar like member.

2. The rock drill according to claim 1 wherein the cylindrical member is made of aluminum alloy.

6 References Cited UNITED STATES PATENTS 6/ 1955 Arnouil 92-172 X 4/ 1957 Wahlsten 92-172 X U.S. Cl. X.R. 92--260 

